White Spot Disease In Shrimp: How To Support Extensive Shrimp Farmers

Shrimp aquaculture is a billion-dollar industry worldwide. It provides about half a billion dollars in export earnings, livelihood, and employment of millions of people in Bangladesh. The mode of shrimp farm operations are mainly extensive in Bangladesh and many south Asian countries. White spot disease (WSD) caused by white spot syndrome virus (WSSV) has been a major threat to shrimp farming for last two decades.

Research and development showed the strategies to control WSD include biosecurity (e.g. exclusion of pathogen from broodstock in hatcheries and farms, zero water exchange, water treatment with disinfectants, probiotics, hygiene and sanitation of the workers, quality diet, and feed management), application of products with antiviral properties, immunostimulants, antimicrobial peptide, vaccinations, and optimum rearing condition.

Application of these strategies in extensive farmers is difficult due to lack of biosecurity, suboptimal rearing conditions, stocking of wild and or untested postlarvae, multiple batches of stocking and harvesting, and irregular feeding. The relationship of WSD outbreak and biosecurity and environmental factors such as temperature, salinity, and farming systems, are well known.

Figure 1: White spot disease-affected shrimp

Several studies in Asia and elsewhere have evaluated the performance of WSSV-negative postlarvae (PL) in intensive monoculture ponds (Withyachumarnkul, 1999; Peng et al., 2001) and provided evidence of the benefits in minimizing WSD-related losses.

In extensive shrimp production systems, multiple stocking and polyculture appeared to be a key resilience strategy. Farmers affected with low shrimp production due to disease tend to reduce the risk by stocking more shrimp, prawn, and fish seed. WSSVF PL stocking had further strengthened the resilience strategy.

The study also highlights why several strict farm-level biosecurity measures, like single stocking and harvesting, monoculture, closed system, and only stocking WSSVF PL, cannot be applied in the context of extensive farms. Further research to understand the interactions of various management interventions, including WSSVF PL, multiple stocking, and polyculture, would help to revisit and refine some of the ongoing practice.